The precision of Ningbo precision casting geometry is determined by the deviation of machining allowance, casting size and weight from the rated amount. Under the same conditions, the geometric accuracy reflects the precision casting from the aspects of machining workload and metal dosage. The advanced level of the processing technology. The tolerance of size and weight and the machining allowance of castings are determined according to the technical conditions of GB6414-86GB/T11351-89GB/T11350-89 and the ordering, respectively, and the actual deviation is determined according to the data of the technical inspection department. The so-called casting size control is to control the degree of dispersion of the measured values under the premise that the measured average value is consistent with the nominal size of the casting. This discrete cause is usually caused by random variations or systematic errors in production technology conditions and raw material characteristics. Precision castings should be judged according to the nature of the error and corresponding countermeasures to improve the dimensional accuracy to meet the requirements of the standard. Sometimes, only one or two dimensions on the entire casting require tighter blank dimensional tolerances, and it is not necessary to have all dimensions to the same level. In order to improve the precision grade of castings, metal molds can generally be used. If it is necessary to significantly improve the modeling method, such as shell casting or other precision casting processes, it will inevitably lead to increased mold costs, prolonged production preparation cycle, and casting costs. Increased exponentially. When assessing the geometry accuracy of castings, the tolerance range or deviation range of the most representative wall thickness and rib thickness shall be given in addition to the allowance of the machining surface and the deviation of the weight of the casting. The wall thickness necessary for the structure is determined by the casting designer and the minimum allowable wall thickness is determined by the casting technologist. In most cases, the decision of the precision casting designer determines the wall thickness marked on the drawing. The tolerance between the design wall thickness and the actual wall thickness is an important indicator to characterize the geometry accuracy of the casting.